"Where are you going to" seems to be quite popular among foreign learners whose mother tongue is German. That's probably because in German, "Where are you going" (wo gehen Sie) would be wrong, the correct form being wo gehen Sie hin. So those people try to mimic that hin in English by adding a to (though, of course, technically hin is not a preposition, but rather a part of the split-up interrogative wohin, "'where' as an indication of direction", as opposed to a simple wo, "'where' as an indication of position, with no indication of direction").
– RegDwigнt♦Nov 2 '10 at 10:28

@Martha: Indeed! That's definitely the coolest way to speak. (Note that you would use "thou" in familiar situations and "you" in formal ones.) Amazingly, "thou" is still somewhat in use in Northern England/Lowland Scotland.
– NoldorinNov 3 '10 at 13:11

Never end a sentence with a preposition, unless you're Winston Churchill. It's occasionally acceptable, but only if the sentence would be horrible if rearranged to avoid it. "Where are you going?" is a fine sentence; the "to" is not needed (either at the beginning or end).

“This is the sort of English up with which I will not put.” ~ Winston Churchill

That quote supports ending sentences with prepositions, which is the opposite of what you're saying. Compare also "Where are you from?" vs. "From where are you?" The former sounds much better.
– ClaudiuNov 4 '10 at 13:51

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